Light-emitting device

ABSTRACT

A light-emitting device comprises a substrate, an epitaxial structure formed on the substrate including a first semiconductor layer, a second semiconductor layer, and a light-emitting layer formed between the first semiconductor layer and the second semiconductor layer. A trench is formed in the epitaxial structure to expose a part of side surface of the epitaxial structure and a part of surface of the first semiconductor layer, so that a first conductive structure is formed on the part of surface of the first semiconductor layer in the trench, and a second conductive structure is formed on the second semiconductor layer. The first conductive structure includes a first electrode and a first pad electrically contacted with each other. The second conductive structure includes a second electrode and a second pad electrically contacted with each other. Furthermore, the area of at least one of the first pad and the second pad is between 1.5×10 4 μm 2  and 6.2×10 4  μm 2 .

BACKGROUND OF THE DISCLOSURE

1. Technical Field

The present invention relates to a light-emitting device, and inparticular to a semiconductor light-emitting device.

2. Reference to Related Application

This application claims the right of priority based on Taiwanapplication Ser. No. 96144680, filed on Nov. 23, 2007, entitled“Light-emitting Device”, and the contents of which are incorporatedherein by reference.

3. Description of the Related Art

The light-emitting mechanism and the structure of a light-emitting diode(LED) are different from that of the conventional light sources. The LEDhas advantages of small size and high reliability, and has been widelyused in different fields such as displays, laser diodes, traffic lights,data storage apparatus, communication apparatus, lighting apparatus, andmedical apparatus.

Referring to FIG. 1A and 1B. FIG. 1A is the schematic top view of aconventional nitride-based light-emitting device 1, and FIG. 1Billustrates a cross-sectional view of the conventional nitride-basedlight-emitting device 1 along the A-A′ line in the FIG. 1A. Theconventional nitride-based light-emitting device 1 includes a substrate11, an n-type nitride-based layer 12, a light-emitting layer 13, ap-type nitride-based layer 14, a p-type transparent electrode 15, ann-type electrode 16 having the function as a bonding pad, and a p-typebonding pad 17. The p-type bonding pad 17 is used for current injection.The current is injected through the p-type bonding pad 17 and moves toand spread through the p-type transparent electrode 15. Electrons andholes recombine in the light-emitting layer 13 and then produce photons.In fact, as shown in FIG. 1B, the current is crowded in the area wherethe p-type transparent electrode 15 is close to the n-type electrode 16to cause a poor light-emitting efficiency. Besides, the temperature inthe current crowded area is so high that the life of conventionalnitride-based light-emitting device 1 is reduced.

In order to resolve above problems, a known art disclosed alight-emitting device 2 which is illustrated by a top view as shown inFIG. 2. Another known art also disclosed a light-emitting device 3 whichis illustrated by a top view as shown in FIG. 3. Referring to FIG. 2,the light-emitting device 2 includes a p-type electrode and an n-typeelectrode. The p-type electrode includes a p-type bonding pad 24, twofirst armed electrodes 24 a extending from the p-type bonding pad 24,and second armed electrodes 24 b interposed between two first armedelectrodes 24 a. The armed electrode can be used to decrease the lightabsorption of the p-type electrode. The current is injected from thep-type bonding pad 24 and spread by the armed electrodes. The n-typeelectrode includes an n-type bonding pad 25, third armed electrodes 25a, and fourth armed electrodes 25 b. The current is injected from thep-type electrode, moves to the light-emitting region of thelight-emitting device 2, and then flows to and out of the n-typeelectrode. The p-type armed electrodes 24 a, 24 b and the n-type armedelectrodes 25 a, 25 b are interdigitated between each other.

Referring to the FIG. 3, the light-emitting device 3 includes an n-typeelectrode having a first contact 35 and an n-type fingered electrode 36connected with the first contact 35 at a first side of thelight-emitting device 3, a p-type electrode having a second contact 37and two fingered electrodes 38 a, 38 b connected with the second contact37 at a second side of the light-emitting device 3, wherein the firstside and the second side are opposite to each other. The n-type fingeredelectrode 36 is extended from the first side to the second side, thep-type fingered electrodes 38 a, 38 b are extended from the second sideto the first side, and the n-type fingered electrode 36 and the p-typefingered electrodes 38 a, 38 b are interdigitated between each other.The light-emitting devices 2 and 3 can resolve the current crowding andlow light efficiency problems of the conventional light-emitting device1 by the interdigitated extending electrodes.

Referring to FIG. 4, further another known art disclosed alight-emitting device 4. The epitaxial structure of the light-emittingdevice 4 includes a spiral-shaped trench, a p-type metal electrode 41located in the exposed surface of the trench, an n-type metal electrode42 located on the un-trenched surface of the epitaxial structure, ap-type bonding pad 43, and an n-type bonding pad 44, wherein the p-typemetal electrode 41 and the n-type metal electrode 42 are parallel anddistributed in spiral shape, which can resolve the current crowding andlow light efficiency problems of the conventional light-emitting device1

In above conventional light-emitting devices, the designs of electrodesadopt transparent electrodes or decrease the electrode area such asarmed, fingered and spiral-shaped electrodes to optimize the lightextraction area. In general, the width of an electrode is designed to besmaller than that of a bonding pad to avoid increasing the lightabsorption area of the electrode.

SUMMARY OF THE DISCLOSURE

Accordingly, this disclosure provides a light-emitting device. Thelight-emitting device comprises a substrate; a light-emitting stackdisposed on the substrate, comprising a first layer, a second layer, anda light-emitting layer disposed therebetween; a trench formed throughthe second layer, the light-emitting layer to the first layer wherein apart of the first layer is exposed; a first conductive structuredisposed on the exposed part of the first layer in the trench; and asecond conductive structure disposed on the second layer; wherein thefirst conductive structure comprises a first electrode and a first padwith an electrical connection formed therebetween; the second conductivestructure comprises a second electrode and a second pad with anelectrical connection formed therebetween; wherein at lease one of thefirst pad and the second pad has an area between 1.5×10⁴ μm² to 6.2×10⁴μm².

This disclosure also provides a light-emitting device comprising asubstrate; a light-emitting stack disposed on the substrate comprising afirst layer, a second layer, and a light-emitting layer disposedtherebetween; a trench formed through the second layer, thelight-emitting layer to the first layer wherein a part of surface of thefirst layer is exposed; a first conductive structure disposed on theexposed surface of the first layer in the trench; and a secondconductive structure disposed on the second layer; wherein the firstconductive structure comprises a first electrode and a first pad with anelectrical connection formed therebetween; the second conductivestructure comprises a second electrode and a second pad with anelectrical connection formed therebetween; wherein at lease one of thefirst pad and the second pad comprises two bonding regions.

This disclosure provides a light-emitting device comprising a substrate;a light-emitting stack disposed on the substrate comprising a firstlayer, a second layer, and a light-emitting layer disposed therebetween;and a first conductive structure disposed on the light-emitting stackwherein the first conductive structure comprises a first electrode and afirst pad with an electrical connection formed therebetween; wherein thefirst pad comprises at least two bonding regions, or the area of thefirst pad is between 1.5×10⁴ μm² to 6.2×10⁴ μm².

This disclosure provides a light-emitting device comprising a substrate;a light-emitting stack disposed on the substrate; and a first electrodeand a first pad with an electrical connection formed therebetween;wherein the area of the first pad is between 3×10⁴ μm² to 1.24×10⁵ μm²and is capable of accommodate at least two wires.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide easy understanding ofthe invention, and are incorporated herein and constitute a part of thisspecification. The drawings illustrate embodiments of the invention and,together with the description, serve to illustrate the principles of theinvention.

FIGS. 1A-1B are a schematic top view and a cross-sectional view of aconventional light-emitting device 1.

FIG. 2 is a schematic cross-sectional view of a conventionallight-emitting device 2.

FIG. 3 is a schematic cross-sectional view of a conventionallight-emitting device 3.

FIG. 4 is a schematic cross-sectional view of a conventionallight-emitting device 4.

FIGS. 5A-5C are a schematic top view and cross-sectional views of alight-emitting device in accordance with a first embodiment of thepresent invention.

FIGS. 6A-6B are a schematic top view and a cross-sectional view of alight-emitting device in accordance with a second embodiment of thepresent invention.

FIG. 7 is a schematic cross-sectional view of a light-emitting device inaccordance with a third embodiment of the present invention.

FIGS. 8A-8B are a schematic top view and a cross-sectional view of alight-emitting device in accordance with a fourth embodiment of thepresent invention.

FIG. 9 is a schematic cross-sectional view of a light source elementincluding a light-emitting device of the present invention.

FIG. 10 is a schematic cross-sectional view of a backlight moduleincluding a light-emitting device of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings. Wherever possible, the same reference numbers are used in thedrawings and the description to refer to the same or like parts.

Referring to FIG. 5A, the schematic top view shows a light-emittingdevice 10 in accordance with a first embodiment of the presentinvention. FIG. 5B illustrates a cross-sectional view of thelight-emitting device 10 along the B-B′ line in the FIG. 5A. Thelight-emitting device 10 such as an LED includes a substrate 100, abuffer layer 110, a first semiconductor layer 120, a light-emittinglayer 130, a second semiconductor layer 140, a first electrode 151, asecond electrode 152, a first and second pad 161 and 162. In theembodiment, the shape of light-emitting device 10 is a rectangular cube.Each side of the light-emitting device 10 is about 610 μm in length. Thearea of the top surface is 3.72×10⁵ μm², and the area of thelight-emitting layer 130 is accorded with the area of the top surface.The buffer layer 110, first semiconductor layer 120, light-emittinglayer 130, and second semiconductor layer 140 are formed on thesubstrate 100 by the method of metal organic chemical vapor deposition(MOCVD) or molecular-beam epitaxy (MBE).

After forming the epitaxial structure, an etching step is performed. Atrench 170 is formed in the epitaxial structure by etching the epitaxialstructure. A part of the first semiconductor layer 120 is exposedthrough the trench 170. The trench 170 is formed in a rectangular spiralshape, and the un-etched epitaxial structure is also formed in arectangular spiral shape.

Next, the first electrode 151 and the first pad 161 are formed on theexposed surface of the first semiconductor layer 120. The shape of firstelectrode 151 is the same as the rectangular spiral shape of the trench170, and the width of the first electrode 151 is about 22 μm. Theposition of first pad 161 can be between two end points of the firstelectrode 151 or in a non-end portion of the first electrode 151. Inthis embodiment, the first pad 161 is disposed at the non-end portion ofthe first electrode 151. Because the light-emitting device 10 has alarger light-emitting area, a larger operating current is necessary fora higher emitting efficiency. In order to achieve the larger amount ofinjected current, more pads area for current injecting are necessary. Inthis embodiment, the area of the first pad 161 is designed to be capableof containing at least two wires for current injecting, and thelight-emitting device has enough wires for current injecting to improvethe light-emitting efficiency. The area of the first pad 161 is 1.9×10⁴μm² in the embodiment.

Further, the second electrode 152 and the second pad 162 are formed andconnected with each other on the remained epitaxial structure. The widthof the second electrode 152 is about 20 μm, and the shape of it is arectangular spiral. The second pad 162 can be situated between two endpoints of the second electrode 152 or on a non-end portion of the secondelectrode 152. In this embodiment, the second pad 162 is situated on thenon-end portion of the second electrode 152. Similarly, in order toachieve a larger injected current, in this embodiment, the area of thesecond pad 162 is designed to be capable of containing at least twowires for current injecting, thus the light-emitting device has enoughamounts of wires for current injecting to improve the light-emittingefficiency. The area of the second pad 162 is 1.73×10⁴ μm² in theembodiment.

The shapes of the first pad 161 and the second pad 162 includerectangular shape, circular shape, or any other shapes. The first pad161 and the second pad 162 including bonding regions are disposed on thefirst and the second electrodes respectively. In the embodiment, bothshapes of the first pad 161 and the second pad 162 are two overlappedcircles. Bonding regions 161A and 161B of the first pad 161, and bondingregions 162A and 162B of the second pad 162 can provide a betteridentification and avoid duplicate bonding of two wires on the same pad.There are wires connecting to the bonding regions 161A, 161B, 162A, and162B respectively so the light-emitting device receives enough currentby wires to have sufficient electrons and holes to recombine and thenemits light. Referring to FIG. 5C, the schematic cross-sectional viewshows a pad 161 with Au bonding bulges 180A and 180B formed on thebonding regions 161A and 161B respectively. During the bonding process,Au bulges are melted by raising temperature, and then the wires 171A and171B are bonded with Au bonding bulges 180A and 180B respectively.Similarly, other two wires are bonded at the bonding regions 162A and162B by the same method.

The direction of the spiral shape is clockwise or counterclockwise, andthe numbers of spiral are not limited. The material of the substrate 100includes but is not limited to sapphire. The material of the bufferlayer 110 includes but is not limited to AIN, AIGaN, or GaN. Thematerial of the first semiconductor layer 120 includes but is notlimited to (Al_(x)Ga_(1-x))_(y)In_(1-y)N wherein 0≦x≦1and 0≦y≦1. Thelight-emitting layer 130 includes but is not limited to a doubleheterostructure or a multi-quantim well including materials such as(Al_(p)Ga_(1-p))_(q)In_(1-q)N wherein 0≦p≦1 and 0≦q≦1.The material ofthe second semiconductor layer 140 includes but is not limited to(Al_(a)Ga_(1-a))_(b)In_(1-b)N wherein 0≦a≦1 and 0≦b≦1.

The material of the first electrode 151 is selected from materials whichcan be formed an ohmic contact with the first semiconductor layer 120,such as a single layer, multiple layers or alloy selected from Ti, Al,and Au, or other metal-oxide conductive material. The first pad 161includes but is not limited to a single layer, multiple layer or alloyselected from Ti, Al, and Au. The material of the second electrode 152is selected from materials which can be formed an ohmic contact with thesecond semiconductor layer 140, such as a single layer, multiple layersor alloy selected from Ni and Au, or other metal-oxide conductivematerial. The second pad 162 includes but is not limited to a singlelayer, multiple layer or alloy selected from Ni and Au.

The areas of the first pad 161 and the second pad 162 do not need tosatisfy the condition of having the area capable of accommodating atleast two wires for current injecting at the same time. It can be one ofthe first pad 161 and the second pad 162 satisfying the condition thatthe area of pad is capable of containing at least two wires.

Referring to FIG. 6A, the schematic top view shows a light-emittingdevice 20 in accordance with a second embodiment of the presentinvention. FIG. 6B illustrates a cross-sectional view of thelight-emitting device 20 along the C-C′ line in the FIG. 6A. Thelight-emitting device 20 includes a substrate 200, an adhesive layer210, a current conductive layer 280, a first semiconductor layer 220, alight-emitting layer 230, a second semiconductor layer 240, a firstelectrode 251, a second electrode 252, a first and second pad 261 and262. In the embodiment, the shape of the light-emitting device 20 is arectangular cube, and the length of each side is about 787 μm. The areaof the top surface is 6.19×10⁵ μm², and the area of the light-emittinglayer 230 is in accord with the area of the top surface. The epitaxialstructure of the light-emitting device 20 is formed on a growthsubstrate (not illustrated). After the epitaxial structure is grown, acurrent conductive layer 280 with a high current conductivity is formedon the first semiconductor layer 220, which can spread the currentinjected from the electrode. Next, the epitaxial structure and thesubstrate 200 are adhered together by the adhesive layer 210.

After the adhering step, a trench 270 is formed in the epitaxialstructure by etching the epitaxial structure. A part of the currentconductive layer 280 is exposed through the trench 270. The trench 270is formed in a fingered shape; the finger is extended from the firstside to the opposite second side of the light-emitting device 20. Theun-etched epitaxial structure also forms a fingered shape.

Next, the first electrode 251 and the first pad 261 are formed on theexposed surface of the current conductive layer 280. The shape of thefirst electrode 251 is the same as the fingered shape of the trench 270,and the first electrode 251 includes at least three linearly extendingelectrodes and a laterally extending electrode connected the threelinearly extending electrodes. The width of the first electrode 251 isabout 23 μm. The first pad 261 can be situated between two end points ofthe first electrode 251 or on a non-end portion of the first electrode251. In this embodiment, the first pad 261 is situated on the non-endportion of the first electrode 251. Similarly, in order to achieve ahigher emitting efficiency, in this embodiment, the area of the firstpad 261 is designed to be capable of containing at least two wires forcurrent injecting so the light-emitting device 20 has enough wires forcurrent injection. The area of the first pad 261 is 2.15×10⁴ μm² in theembodiment.

Further, the second electrode 252 and the second pad 262 are formed andconnected with each other on the remained epitaxial structure. Thesecond electrode 252 includes three linearly extending electrodesextended from the second side to the opposite first side of thelight-emitting device 20, and interdigitated between the three linearlyextending electrode of the first electrode 251, and a laterallyextending electrode connecting the three linearly extending electrodes.The width of the second electrode 252 is about 20 μm. The second pad 262is disposed at the second side and connected with the second electrode252. The area of the second pad 262 is 1.27×10⁴ μm² in the embodiment.

In this embodiment, the shape of the second pad 262 is rectangular, andthe second pad 262 is situated on the non-end portion of the secondelectrode 152. The first pad 261 is capable of containing two bondingregions 261A and 261B. Each of regions 261A and 261B electricallyconnects to at least a wire for bonding, such that a betteridentification can be achieved for the next bonding procedure to avoiddifferent wires being bonded at the same bonding region. The second pad262 has a circular shape, and only one bonding region 262A whichconnects to a wire electrically. The area of the second pad 262 is alsocan be designed as an size containing at least two wires, such as thearea of the second pad 262 is 1.5×10⁴ μm².

The material of the growth substrate includes but is not limited tosapphire, SiC, GaN, GaAs, or GaP. The material of the substrate 200includes but is not limited to SiC, GaN, GaP, Si, AIN, ZnO, MgO,MgAl₂O₄, GaAs, glass, sapphire, metal, or compound materials. Theadhesive layer 210 includes a conductive adhesive layer or an insulatingadhesive layer. The material of the conductive adhesive layer includesbut is not limited to Ag, Au, Al, In, or Sn, or alloy of them,spontaneous conductive polymer, or polymer doped with metal like Al, Au,Pt, Zn, Ag, Ni, Ge, In, Sn, Ti, Pb, Cu, Pd, or other metals . Thematerial of the insulating adhesive layer includes but is not limited tospin on glass (SOG), silicone, benzocyclobutene (BCB), epoxy, polyimide(PI), or perfluorocyclobutane (PFCB). When the adhesive layer 210 is theinsulating adhesive layer, the material of the substrate 200 is notlimited. In the embodiment, the material of the substrate 200 is Si. Thematerial of Si has a higher heat transfer coefficient to transfer theheat produced by the light-emitting device to the environment. Areflective layer 211 is further disposed on one side of the adhesivelayer 210. The material of the reflective layer 211 includes but is notlimited to metal, oxide, or the combination thereof. The oxide materialfor the reflective layer 211 includes but is not limited to AlO_(x),SiO_(x), or SiN_(x).

When the adhesive layer 210 is the conductive adhesive layer, thematerial of the substrate 200 includes but is not limited to glass,sapphire, or AIN. It also can disposes an insulating layer between thecurrent conductive layer 280 and the adhesive layer 210, or the adhesivelayer 210 and the substrate 200, wherein the material of the substrate200 is not limited. Referring to FIG. 7, a cross-sectional view shows alight-emitting device in accordance with a third embodiment of thepresent invention. FIG. 7 illustrates an insulating layer 690 disposedbetween the adhesive layer 210 and the current conductive layer 280 forisolation. The material of the insulating layer includes but is notlimited to SiN_(x) or SiO₂. The material of the first semiconductorlayer 220 includes but is not limited to (Al_(m)Ga_(1-m))_(r)In_(1-r)Nwherein 0≦m≦1 and 0≦r≦1 or(Al_(c)Ga_(1-c))_(d)In_(1-d)P wherein 0≦c≦1and 0≦d≦1. The light-emitting layer 230 includes but is not limited to adouble heterostructure or a multi-quantum well including materials suchas (Al_(e)Ga_(1-e))_(f)In_(1-f)N wherein 0≦e≦1 and 0≦f≦1or(Al_(i)Ga_(1-i))_(j)In_(1-j)P wherein 0≦i≦1 and 0≦j≦1. The material ofthe second semiconductor layer 240 includes but is not limited to(Al_(k)Ga_(1-k))_(h)In_(1-h)N wherein 0≦k≦1 and 0≦h≦1 or(Al_(s)Ga_(1-s))_(t)In_(1-t)P wherein 0≦s≦1 and 0≦t≦1.

The material of the first electrode 251 includes but is not limited to asingle metal layer, multiple metal layers or alloy of Ni, and Au, orother conductive metal oxide layer. The material of first pad 261includes but is not limited to a single metal layer, multiple metallayers or alloy of Ni, and Au. The material of the second electrode 252includes but is not limited to a single metal layer, multiple metallayers or alloy of Ti, Al, and Au, or conductive metal oxide layer. Thesecond pad 262 includes but is not limited to a single metal layer,multiple metal layers or alloy of Ti, Al, and Au. The shapes of thefirst electrode 251 and the second electrode 252 include M linearlyextending electrodes respectively, wherein M≧1. The first electrode 251can include M linearly extending electrodes, wherein M≧1, and the secondelectrode 252 includes M−1 linearly extending electrodes.

Referring to FIG. 8A, the schematic top view shows a light-emittingdevice 30 in accordance with a fourth embodiment of the presentinvention. FIG. 8B illustrates a cross-sectional view of thelight-emitting device 30 along the D-D′ line in the FIG. 8A. Thestructure of the light-emitting device 30 is similar to that of thelight-emitting device 10 including a substrate 100, a buffer layer 110,a first semiconductor layer 120, a light-emitting layer 130, and asecond semiconductor layer 140. After forming the epitaxial structure, acurrent conductive layer 380 is disposed on the second semiconductorlayer 140. In the embodiment, the light-emitting device 300 is arectangular cube and the length of each side of the light-emittingdevice 30 is about 1143 μm. The area of the top surface is 1.31×10⁶ μm²,and the area of the light-emitting layer 130 is in accord with the areaof the top surface.

After the step of forming the current conductive layer 380, an etchingstep is performed. A trench 370 is formed in the current conductivelayer 380 and the epitaxial structure by etching part of them. A part ofthe first semiconductor layer 120 is exposed through the trench 370. Theshape of the trench 370 is formed in a pair of spiral, and the un-etchedcurrent conductive layer 380 and epitaxial structure are also formed ina pair of spiral shape.

Referring to FIG. 8A, the light-emitting device 30 includes a pair offirst electrodes 351A and 351B and a pair of second electrodes 361A and361B formed in a pair of spiral shape respectively. After the trench 370is formed, the first electrodes 351A and 35 1B, and first pads 361A and361B are formed on the exposed surface of the first semiconductor layer120. The shape of first electrodes 351A and 351B are the same as thepair of spiral shape of the trench 370. The width of the firstelectrodes 351A or 351B is about 10 μm respectively. First pads 361A and361B can be situated between two end points of first electrodes 351A and351B or on a non-end portion of first electrodes 351A and 351B. In thisembodiment, first pads 361A and 361B are situated on the non-endportions of first electrodes 351A and 351B near a first side of thelight-emitting device 30 and a second side opposite to the first side.The area of first pad 361A and 361B are the same as 1.9×10⁴ μm².

Further, the second electrodes 352A and 352B, and the second pad 362 areformed on the remained current conductive layer 380. The width of thesecond electrode 352A or 352B is about 10 μm respectively. The secondelectrodes 352A and 352B are formed in a spiral shape and connected withthe second pads 362 respectively. The second pad 362 can be disposed ata third side neighboring with the first side and the second side, andconnect to second electrodes 352A and 352B. In this embodiment, the areaof the second pad 362 is designed to be capable of containing at leasttwo wires for current injection so the light-emitting device 30 hasenough current to higher brightness. The area of the second pad 362 is1.9×10⁴ μm² in the embodiment.

In the embodiment, the shape of the second pad 362 formed as two circlespartially overlapped includes two bonding region 362A and 362B such thata better identification can be achieved for the next bonding procedureto avoid two wires being bonded on the same bonding region. There arewires connecting to the bonding regions 361A, 361B, 362A, and 362Brespectively, so the light-emitting device 30 receives enough current bywires to have sufficient electrons and holes to recombine and then emitslight. The shape of the light-emitting device 30 includes but is notlimited to a square shape or a rectangular shape. The material of thecurrent conductive layers 280 and 380 includes but is not limited toindium tin oxide, cadmium tin oxide, zinc oxide, or zinc tin oxide. Eachsurface of the light-emitting device can be a rough surface by anepitaxial or an etching process, such as a rough surface around thesubstrate or around the epitaxial structure, a rough surface in the toplight extraction surface, or a rough surface under and contact with theelectrode, to improve the light extraction efficiency.

Referring to FIG. 9, the schematic cross-sectional view shows a lightsource apparatus 90 in accordance with a fifth embodiment of the presentinvention. The light source apparatus 90 includes a light-emittingdevice of above embodiments. The light source apparatus 7 is a lightingapparatus such as streetlamps, vehicle lamps, or indoor lightings. Italso can be traffic lights or backlights of a module in a planardisplay. The light source apparatus 90 includes a light source 910 withthe light-emitting device of above embodiments, a power supply system920, and a control element 930 for controlling the power supply system920.

Referring to FIG. 10, the schematic cross-sectional view shows abacklight module 100 in accordance with an eighth embodiment of thepresent invention. The backlight module 100 includes the light sourceapparatus 90 and an optical element 1010. The optical element 1010 isused to operate the light emitted from the light source apparatus 90 tosatisfy the requirements of the backlight. The optical element 1010includes a photonic lattice, a color filter, a wavelength conversionlayer, an antireflective layer, a lens or the combination thereof.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the structure of the presentinvention without departing from the scope or spirit of the invention.In view of this, it is intended that the present invention coversmodifications and variations of this invention provided they fall withinthe scope of the following claims and their equivalents.

1. A light-emitting device comprising: a substrate; a light-emittingstack disposed on the substrate, comprising a first layer, a secondlayer, and a light-emitting layer disposed therebetween; a trench formedthrough the second layer, the light-emitting layer to the first layerwherein a part of the first layer is exposed; a first conductivestructure disposed on the exposed part of the first layer in the trench;and a second conductive structure disposed on the second layer; whereinthe first conductive structure comprises a first electrode and a firstpad with an electrical connection formed therebetween; the secondconductive structure comprises a second electrode and a second pad withan electrical connection formed therebetween; wherein at least one ofthe first pad and the second pad has an area between 1.5×10⁴ μm² to6.2×10⁴ μm², and the shape thereof comprises two partially overlappedcircles.
 2. A light-emitting device according to claim 1, wherein thefirst layer comprises a first conductive semiconductor layer and thesecond layer comprises a second conductive semiconductor layer.
 3. Alight-emitting device according to claim 1, wherein at least one of thefirst pad and the second pad has an area between 1.5×10⁴ μm² to 3×10⁴μm².
 4. A light-emitting device according to claim 1, wherein at leastone of the first pad and the second pad comprises at least two bondingregions when the first and/or second pad has an area between 1.5×10⁴ μm²to 6.2×10⁴ μm².
 5. A light-emitting device according to claim 4, furthercomprising at least two wires connect with the two bonding regionsrespectively.
 6. A light-emitting device according to claim 1, whereinthe first layer comprises a current conductive layer, and asemiconductor layer is formed between the current conductive layer andthe light-emitting layer.
 7. A light-emitting device according to claim6, the current conductive layer comprising at least one materialselected from the group consisting of indium tin oxide, cadmium tinoxide, zinc oxide, and zinc tin oxide.
 8. A light-emitting deviceaccording to claim 6, further comprising an adhesive layer between thecurrent conductive layer and the substrate.
 9. A light-emitting deviceaccording to claim 8, wherein the adhesive layer is selected from thegroup consisting of an insulating adhesive layer and a conductiveadhesive layer.
 10. A light-emitting device according to claim 9,wherein the insulating adhesive layer comprises at least one materialselected from the group consisting of spin on glass (SOG), silicone,benzocyclobutene (BCB), epoxy, polyimide (PI), and perfluorocyclobutane(PFCB).
 11. A light-emitting device according to claim 9, wherein theconductive adhesive layer comprises at least one material selected fromthe group consisting of Ag, Au, Al, In, Sn, and alloy of them,spontaneous conductive polymer, and polymer doped with metal like Al,Au, Pt, Zn, Ag, Ni, Ge, In, Sn, Ti, Pb, Cu, Pd or alloy of them.
 12. Alight-emitting device according to claim 9, further comprising areflective layer disposed on one side of the adhesive layer.
 13. Alight-emitting device according to claim 1, wherein at least one of thefirst electrode and the second electrode is distributed in a linearlyextending structure, and the linearly extending structure is continuouswithout any branch.
 14. A light-emitting device according to claim 13,wherein the linearly extending structure is selected from the groupconsisting of curve and straight line.
 15. A light-emitting deviceaccording to claim 14, wherein the first pad or the second pad issituated on a non-ending portion of the linearly extending structure.16. A light-emitting device according to claim 14, wherein the linearlyextending structure comprises a spiral structure.
 17. A light-emittingdevice according to claim 1, wherein the substrate comprises at leastone material selected from the group consisting of sapphire, GaN, AIN,SiC, GaAs, GaP, Si, ZnO, MgO, MgAl₂O₄, glass, metal, and compoundmaterial.
 18. A light-emitting device according to claim 1, wherein thewidth of the first electrode and/or the second electrode is smaller thanor equal to 25 μm.
 19. A light-emitting device according to claim 18,wherein the width of the first electrode and/or the second electrode issmaller than or equal to 10 μm.
 20. A light-emitting device comprising:a substrate; a light-emitting stack disposed on the substrate comprisinga first layer, a second layer, and a light-emitting layer disposedtherebetween; a trench formed through the second layer, thelight-emitting layer to the first layer wherein a part of the firstlayer is exposed; a first conductive structure disposed on the exposedpart of the first layer in the trench; and a second conductive structuredisposed on the second layer; wherein the first conductive structurecomprises a first electrode and a first pad with an electricalconnection formed therebetween; the second conductive structurecomprises a second electrode and a second pad with an electricalconnection formed therebetween; wherein at least one of the first padand the second pad comprises two bonding regions, and the shape thereofcomprises two partially overlapped circles.
 21. A light-emitting devicecomprising: a substrate; a light-emitting stack disposed on thesubstrate comprising a first layer, a second layer, and a light-emittinglayer disposed therebetween; and a first conductive structure disposedon the light-emitting stack; wherein the first conductive structurecomprises a first electrode and a first pad with an electricalconnection formed therebetween; wherein the first pad comprises at leasttwo bonding regions or the area of the first pad is between 1.5×10⁴ μm²to 6.2×10⁴ μm², and the shape of the first pad comprises two partiallyoverlapped circles.
 22. A light-emitting device according to claim 21,further comprising: a trench formed through the second layer, thelight-emitting layer to the first layer, wherein a part of surface ofthe first layer is exposed; and a second conductive structure disposedon the second layer; wherein the second conductive structure comprises asecond electrode and a second pad with an electrical connection formedtherebetween; wherein the second pad comprises at least two bondingregions or the area of the second pad is between 1.5×10⁴ μm² to 6.2×10⁴μm², and the shape of the second pad comprises two partially overlappedcircles.
 23. A light-emitting device comprising: a substrate; alight-emitting stack disposed on the substrate; and a first electrodeand a first pad with an electrical connection formed therebetween;wherein the area of the first pad is between 3×10⁴ μm² to 1.24×10⁵ μm²and is capable of accommodating at least two wires, and the shape of thefirst pad comprises two partially overlapped circles.